It is commonly known to incorporate pre-printed polymer oblates in items such as cups or lids with a view to give the items a trusted and qualitatively attractive exterior.
This technology is typically used for items such as cups and lids as food packaging where items are manufactured in an injection press in which the pre-printed oblate is conveyed to the injection press and thereby integrated into the workpiece when it is molded.
A pre-printed polymer oblate which is integrated into an item that is injection casted is often referred to as an Inmould Label abbreviated IML.
IML is a plastic film which is typically printed in a so-called flexo printing machine. After printing, a film is laminated onto the product in order to confine the pressure since the material, as mentioned earlier, is often used for packaging in the food industry.
The currently known technology and the method of handling the IML for the conveyance of the oblates to a molding machine such as an injection press typically comprise the following:
Following lamination, the product is punched with a contour that is matched to the application. After punching, the remaining grid is rolled-up or removed by suction. The individual products are supplied in layers on a conveyor. At this stage of production, the individual products are heavily charged with static electricity, which makes it impossible to assemble products in an acceptable stack for the injection press.
Static electricity occurs when the products are punched out of the web. A lot of effort is put into preventing this condition; for example by adding charged ions to the web before punching. However, this is not sufficient to prevent the static electricity.
From the supply conveyor, the products are stacked to the extent possible—and placed on pallets which are then stocked. After a couple of days, the static electricity is minimised, and the pallet is retrieved. It is now possible to create proper stacks that can be used for injection casting.
The IML stack is placed in a magazine. A handling robot collects an IML by means of vacuum and places it in the injection molding tool. Here, it is necessary to supply static electricity to the IML so that it can hook onto the tool until this is closed and ready for molding.
The print shop has striven to eliminate static electricity from IML, whereas static electricity must be supplied to the IML during the molding process to enable the IML to attach itself to the molding tool. The fact that the print shop has removed static electricity relatively efficiently, makes it hard to reload the IML.
Another method is to cut the web into sheets. This way, it is possible to create a stack; however, the air between the sheets must be pressed out before storage. In a so-called guillotine, the products are cut into squares. Each stack is pressed through a “sausage roller” into the final shape. This method is problematic, however, since the products tend to coalesce along the edge.
The currently known and most widely used technology has some drawbacks including the following:
It requires a lot of labour and resources to produce a stack of IML oblates
Cutting out the individual IML generates a relatively large amount of waste material
It is difficult and costly to manage static electricity
The initial investment in equipment for the production of IML is relatively large and often constitutes up to one million Euros.